From the book Neoplatonism:

Plotinus’s model includes three “hypostases,” or fundamental levels of reality. The first and highest is the unknowable “One,” which emanates the next level, called Nous, translated as Divine Mind or Intelligence. This second level contains the Platonic Forms or Ideas, which we can know intellectually, and so this level is also called the Intelligible World. Nous then emanates the next lower level, Psychē or Soul, which animates the physical world and serves as an intermediary between the Intelligible World and the material world we know with our physical senses.

In Neoplatonism, the universe was divided fundamentally between the highest good (the One), the unchangeable realm known as the “Intellect”, and finally the material world or “Soul”. The highest level of existence was considered pure actuality, or pure act, or pure aseity. This realm could in no fashion be related to other forms of being, but was timeless, immutable, impassible, and ineffable. The second level was the Intellect, with which all good philosophers strove to re-achieve union. The material world was the world of the soul, in which philosophers had to escape through ascension. The early Church fathers became infatuated with this strain of Neoplatonism, in which the material world was separate and unrelated to the highest Good, which they equated with God.

Augustine, particularly, was a strong adherent to Neoplatonism (in this tradition). His conversion to Christianity recognized what he saw as a distinction between Neoplatonism and what he considered Christianity. He saw Jesus as the enabling spark which connects the various realms and helps guide the Soul back to merge with the Intellect, without which the bridge could not be made. Jesus was the key to ascension to the changeless realm.

Jesus, in this view, has an element of the One in himself (often described by modern adherents as a mystery one just has to accept). Recall, the One cannot be in relation to anything else. The One is beyond description or intelligibility; no positive attributes can be said of the One. This, in modern circles is called the Hypostatic union.

Adherents to the idea of the Hypostatic Union will talk about two natures of Christ (the natural and divine), and differentiate Jesus from Christ (as White does in the Enyart debate). They will also be hesitant to call “divine” the human nature of Jesus. Divinity in Neoplatonism, can have nothing to do with the changing material world. In this way, the concept of the Hypostatic Union is a Neoplatonistic mechanism for bridging the hypostases, while trying to maintain them as distinct.